Technical Abstract:
The soil carbon (C) pool constitutes the largest reservoir of C in terrestrial ecosystems. Full accounting of C emissions and sequestration to obtain net C flux budgets for agriculture indicate that agricultural land can function as a net source or sink of C, depending on land use and management. Adoption of land management strategies that foster C sequestration in agricultural soils will be important over the next several decades as we develop new mitigation strategies and technologies to reduce C emissions. The objective of this chapter is to provide a broad overview of C cycling in agroecosystems and to discuss selected research focus areas that challenge current paradigms and address the current state of our knowledge. Agricultural land management options currently recommended to foster C sequestration nearly always include some reduction in tillage intensity and implementation of integrated, multifunctional cropping rotations that include forage legumes, small grains and organic amendments from animal manure or compost, supporting the production of primary commodity crops (corn, soybean, wheat, rice, and cotton). For example, planting cover crops after harvesting primary crops, can extend the time that atmospheric carbon dioxide is captured and stored in plant biomass. Increasing CO2 levels in the atmosphere can increase the amount of plant biomass and can potentially increase the rate of soil carbon sequestration. There is a linkage between carbon dynamics and the loss of other greenhouse gases, e.g., methane and nitrous oxide, from soil. Methane is linked with soil biological processes in high organic matter soils while nitrous oxide is related to nitrogen dynamics linked to water status in soils. The challenges for agroecosystem management are to determine the dynamics of soil carbon under different cropping and soil management practices. Improvement of soil organic matter content has major benefits in enhancing the soil function and capabilities. The interest in carbon sequestration as part of carbon balance has to be balanced with improvements in the soil that promote healthy ecosystems.